低地板電動大客車底盤之結構分析與最佳化設計

Abstract

本文研究低地板電動大客車底盤之結構分析，並提出對於低地板電動大客車底盤的結構設計與最佳化之方法，以改良靜態結構特性。藉由靜態有限元素分析方法分析大客車底盤的結構特性，本研究對大客車底盤所考慮的靜態有限元素分析包括全負載應力、彎曲剛性及扭矩剛性分析。更改設計的目地是為了以最小重量來提升大客車底盤的強度和剛性，藉由兩階段最佳化來改良複雜的大客車底盤結構。在第一階段最佳化，選取在少數高應力集中位置周圍的元件，接下來計算相關的元件厚度對於被選取元件的應力和重量的敏感度，選取具有較高的應力對重量之敏感比例的元件厚度做為設計變數，然後執行結構最佳化以藉由最小的上升重量來降低高應力集中區域；在第二階段最佳化，選取不在高應力集中位置周圍的較厚元件，接下來計算相關的元件厚度對於被選取元件的剛性和重量的敏感度，選取具有較低的剛性對重量之敏感比例的元件厚度做為設計變數，然後執行結構最佳化來減低底盤重量並保持改良後的強度和原來的剛性；最後，比較原來的和改良的底盤結構的靜態結構特性，並顯示出改良後的底盤為較佳的結構設計。

This paper studies the structural analyses of a low-floor electrical bus chassis and presents a method for structural design and optimization of a low-floor electrical bus chassis for improving static structural characteristics. The structural characteristics of the bus chassis are analyzed by static finite element analysis method. The static finite element analyses considered in this research include full-loaded stress, bending stiffness and torsional stiffness analyses for the bus chassis. The redesign purpose is to increase the strength and stiffness of the bus chassis with minimum weight. The complex bus chassis structure is improved by two stage optimizations. In the first stage optimization, components in the neighbor of few locations with high stresses are selected, and then sensitivities of stress and weight of selected components with respect to component thicknesses are computed. Component thicknesses with high sensitivities ratio of stress to weight are chosen as design variables. Then the structural optimization is performed to reduce the high stress regions with minimum increased weight. In the second stage optimization, thick components not in the neighbor of the locations with high stresses are selected, and then sensitivities of stiffness and weight of selected components with respect to component thicknesses are computed. Component thicknesses with low sensitivities ratio of stiffness to weight are chosen as design variables. Then the structure optimization is performed to reduce the chassis weight while maintaining the improved strength and original stiffness. Finally, static structural characteristics of the original and improved chassis structures are compared, and it shows that the improved chassis is a better structural design.